"OPTICAL RECORDING MEDIUM"

Abstract

The invention discloses an optical recording medium having a transparent substrate 1, a first protective layer 2, a recording layer 3, a second protective layer 4 , a sulfidation prevention layer 5, and a reflective layer 6, wherein the recording layer 3 comprises Ga, Sb, Sn and Ge, and where the transfer linear velocity is 20 m/s to 30 m/s, wherein the wavelength of a recording and reproducing light is 650 nm to 665 nm and the recording linear velocity is 20 m/s to 28 m/s, the refractive index Nc and the extinction coefficient Kc in a crystalline state and the refractive index Na and the extinction coefficient Ka in an amorphous state in the recording layer respectively satisfy 2.0&#8804; Nc&#8804; 3.0, 4.0&#8804; Kc&#8804; 5.0, 4.0&#8804; Na&#8804; 5.0, and 2.5&#8804; Ka&#8804; 3.1, the sulfidation prevention layer 5 has a mixture of TiC and TiO.

Full Text

Technical Field
The present invention relates to a phase-change optical
recording medium (such as, DVD-RW, DVD+RW or DVD-RAM)
where the irradiation of laser beam causes optical changes to a
recording material of a recording layer therefore information is
recorded and reproduced; and the information is rewritable, and
relates specifically to an optical recording medium having
performance responsive to high-speed recording linear velocity,
as well.
Background Art
Conventionally, in a phase-change optical recording
medium where information is recorded and reproduced onto/from
a recording layer and the information is rewritable, the recording
layer contains four elements, Ag, In, Sb and Te, as primary
components. The objective is to improve the recording linear
velocity on the basis of stable signal processing, making it
possible to stably perform recording and. reproducing at IX-speed
to 4X-speed of a recording linear velocity of DVD-ROM (3.49 m/s),
which is now commercially available.
In the optical recording medium, the manner in which to

conduct heat subtly changes depending upon an optical constant
or film thickness of each layer laminated on a substrate, and may
greatly affect the recording characteristic in a mark recorded on
the recording layer, or reflectance or modulation factor may
change. As in Patent Literature 1, the film thickness of each
layer laminated onto a substrate, an optical constant of a
crystalline phase and an amorphous phase in the recording layer,
an optical constant regarding a protective layer and a reflective
layer, and the condition for groove depth of a transparent
substrate are important factors relating to recording
characteristics and signal processing.
In addition, in order to realize high-speed recording,
recording must be performed with additionally higher power, so
the storage reliability becomes more severe than in comparison
with the conventional art. Using Ag having high thermal
conductivity for a reflective layer binds with S in ZnS-SiO2 of a
protective layer and Ag2S is formed, so it is necessary to establish
a sulfidation prevention layer between the reflective layer and
the protective layer. However, recording with higher power
causes the easy occurrence of peeling-off with interference
between the Ag reflective layer and the sulfidation prevention
layer, leading to the problem that a disc defect easily occurs after
repeated recording or after long-term storage in a severe

environment.
As a related well-known technology, Patent Literature 2
discloses an invention where tantalum oxide, tantalum and
nickel are used for an intermediate layer making contact with an
Ag reflective layer, and Mw(SbzTe1-z)1-w provided that 0 ≤ w ≤ 0.3
and 0.5 ≤ z ≤ 0.9, for a recording layer. However, the invention
has different constituent elements from those in the sulfidation
prevention layer of the present invention," and in addition,
recording is performed at 2X-speed of CD (2.4 m/s), which is at a
lower velocity, and lower density compared to those in the
present invention.
Further, Patent Literature 3 relating to the present
application by the applicant discloses an invention where Si, SiC,
Ge and GeCr are used for a sulfidation prevention layer making
contact with an Ag reflective layer, and GaaGeBInySbSTee
(provided that 0
s
different constituent elements from those in the sulfidation
prevention layer of the present invention. In addition,
recording is performed at 20 m/s at maximum, which is at a lower
velocity compared to that of the present invention.
Further, Patent Literature 4 discloses an invention where
a recording lasher composed of GeSbln, and recording is performed

at 2.4 m/s to 9.6 m/s, which is at a lower velocity compared to that
in the present invention.
The present invention is directed at providing a DVD+RW
recordable at 6X-speed to 8X-speed of DVD-ROM (hereafter,
simply referred to as '6X-speed to 8X-speed), and optical
constants in a crystalline state and an amorphous state in a
recording layer, and the groove condition to control high
reflectance are studied; concurrently, the sulfidation prevention
layer is also studied.
Patent Literature 1" Japanese Patent Application Laid-Open
(JP-A) No. 2000-76702
Patent Literature % Japanese Patent (JP-B) No. 3494044
Patent Literature 3" Japanese Patent Application Laid-Open
(JP-A) No. 2003-248967
Patent Literature 4: Japanese Patent Application Laid-Open
(JP-A) No. 2001-39031
Disclosure of Invention
The objective of the present invention is to provide a
DVD+RW medium repeatedly recordable at a high linear velocity,
20 m/s to 28 m/s (approximately 6X-speed to 8X-speed), and
where recording characteristic and storage characteristic are also
excellent. Further, the objective is to provide a DVD+RW

medium where the reflectance of the recording layer is appropriately reduced.
In addition, the objective is to provide a phase-change optical recording medium
where it becomes difficult for disc defects to occur due to loose film to occur even
after repeated recording or long-term storage in a severe environment by the
improvement of adhesion between the reflective layer and the sulfidation
prevention layer.
The above-mentioned problems are resolved by the following inventions 1) to
11) (hereafter, referred to as Inventions 1 to 11).
l) An optical recording medium comprising-'
a transparent substrate,
a first protective layer disposed on the transparent substrate,
a recording layer disposed on the first protective layer,
a second protective layer disposed on the recording layer, and
a reflective layer disposed on the second protective layer,
wherein when the wavelength of a recording and reproducing light is
within the range of 650 nm to 665 nm and the recording linear velocity is 20 m/s
to 28 m/s, the refractive index Nc and the extinction coefficient Kc in a
crystalline state and the refractive index Na and the extinction coefficient Ka in
an amorphous state in the recording layer respectively satisfy the following
numerical expressions:
2.0 ≤Nc ≤ 3.0,
4.0 ≤ Kc ≤ 5.0,

4.0 ≤ Na ≤ 5.0, and
2.5≤Ka≤3.1, and
wherein information is recordable at the range of 20 m/s to 28 m/s of
recording linear velocity,
wherein the optical recording medium comprises a sulfidation
prevention layer between the second protective layer and the reflective layer;
and the first protective layer and the second protective layer comprises a
mixture of ZnS and Si02, respectively, characterized in that the sulfidation
prevention layer comprises a mixture of TiC and TiO, and the recording layer is
composed of a phase-change recording material comprising Ga, Sb, Sn and Ge,
and the transfer linear velocity is 20 m/s to 30 m/s,
2) The optical recording medium according to 1), wherein when the
mutual composition ratios (atomic%) of the four elements, Ga, Sb, Sn and Ge, in
the recording layer are regarded as a, 6, y and 8, respectively, these satisfy the
following numerical expressions: 2 ≤ a ≤ 11, 59 ≤ 6 ≤ 70, 17 ≤ y ≤ 26, 2 ≤ 8 ≤ 12,
84 ≤ 6 + y ≤ 88, and a + 6 + y + 8 = 100.
3) The optical recording medium according to 2), wherein the total of
contents of the four elements, Ga, Sb, Sn and Ge, in the recording layer is 95
atomic% or greater relative to all elements in the recording layer.
4) The optical recording medium according to 3), wherein the recording
layer further comprises Te.
5) The optical recording medium according to any of 1) to 4), wherein the

film thickness of the first protective layer is 30 nm to 100 nm, the film thickness
of the recording layer is 5 nm to 50 nm, the film thickness of the second
protective layer is 3 nm to 15 nm and the film thickness of the reflective layer is
100 nm to 300 nm.
6) The optical recording medium according to any of 1) to 5), wherein the
transparent substrate has a wobbled groove with 0.74 ± 0.03 µm of track pitch,
22 nm to 40 nm of groove depth and 0.2 µm to 0.3 µm of groove width.
7) The optical recording medium according to 6), wherein the total film
thickness of the second protective layer and the sulfidation prevention layer is 7
nm to 20 nm.
8) The optical recording medium according to 6), wherein the total film
thickness of the second protective layer and the sulfidation prevention layer is 7
nm to 15 nm.
9) The optical recording medium according to any of l) to 8), wherein the
composition of the sulfidation prevention layer is (TiC)p(TiO)ioo-p; wherein 'p'
represent percentage by mass and satisfy the following numerical expressions,
50 ≤p ≤ 80.
10) The optical recording medium according to any of 1) to 9), wherein the
optical recording medium further comprises a layer containing a mixture of
Zr02, Y203, and Ti02 with 2 nm to 8 nm of film thickness between the second
protective layer and the sulfidation prevention layer.
11) The optical recording medium according to any of 1) to 10), wherein the

optical recording medium further comprises a layer containing Si02 with 2 nm
to 4 nm of film thickness between the first protective layer and the phase-
change recording layer.
Brief Description of Accompanying Drawings
Fig. 1 is a chart showing the comparison result of storage stability of
reflectance after the initialization of recording materials Ga5Sb70Sn17Ge8 and
Ga11.9Sb73.1Sn15.0
Fig. 2 is a chart showing the storage characteristic of recording medium
having recording material of Ge5Sb70Sn17Ge8 which shows jitter characteristic
after initial recording and overwriting.
Fig. 3 is a diagram showing a layer construction example of the optical
recording medium of the present invention.
Fig. 4 is a comparison chart of recording characteristic regarding the total
composition ratio (atomic%) of Sb to Sn in Examples A-2, A-20 and A-21.
Fig. 5 is a chart showing the comparison result of DC jitter in Examples A-3,
A-24 and A-25.
Fig. 6 is a chart showing the comparison result of

modulation factor in Examples A-3, A-24 and A-25.
Fig. 7 is a chart showing the comparison result of
reflectance at an unrecorded part in Examples A-3, A-24 and
A-25.
5 Fig. 8 is a chart showing the experimental result of
composition dependency of Sb + Sn in the recording characteristic
of GaSbSnGe-base material at 8X-speed.
Fig. 9 is a chart showing the evaluation result of the
optical recording medium in Example B-l.
Fig. 10 is a chart showing the evaluation result of the
optical recording medium in Example B"2.
Best Mode for Carrying Out the Invention
The present invention is described hereafter.
In the optical recording medium of the present invention,
a first protective layer; a recording layer composed of a
phase-change recording material comprising at least four
elements, Ga, Sb, Sn and Ge, and where a transfer linear velocity
is 20 mg/s or faster; a second layer; and a reflective layer are
laminated onto a transparent substrate in this order. The
transfer linear velocity is a physical quantity substituting a
crystallization kinetic unique to each phase-change recording
material, and herein, it indicates a velocity where the reflectance

starts decreasing rapidly in the case of researching the scanning
speed dependency of crystalline reflectance by irradiating a
continuous light with 18 mW. If a phase-change recording
material where the transfer linear velocity is 20 m/s or faster is
used, no amorphousness is occurred even though a light is
continuously irradiated while the optical recording medium is
rotated at less than 20 m/s. Further, if a phase-change
recording material where the transfer linear speed is 30 m/s or
slower is used, the amorphousness can be easily conducted at
approximately 6X-speed to 8X-speed of the recording linear
velocity. If the transfer linear velocity becomes faster than this,
the amorphousness becomes difficult and recording becomes
difficult.
As a recording material of the recording layer, a
phase-change recording material responsive to the recording
linear velocity at approximately 6X-speed to 8X_speed is
required.
In the present invention, it is essential to record an
amorphous mark more securely than the case of recording the
mark at lX-speed to 4X-speed, and for the absorption coefficient
in the crystalline state of the recording layer, the higher the
better. However, if it is excessively high, the remaining heat is
filled and characteristic deteriorates. Further, for the refractive

index in the amorphous state, the greater the better. There is a
report that it is desirable that the refractive index & the
extinction coefficient in the crystalline state and the refractive
index & the extinction coefficient in the amorphous state in the
AglnSbTe-base phase-change recording material, which is a
conventional phase-change recording material, are within the
range of 2 to 4, 2 to 4, 2.5 to 4 and 2.5 to 3.5, respectively (Patent
Literature l). As result of researching the GaSbSnGe-base
phase-change recording material with reference to these findings
by the inventors of the present application, the result shown in
the below-described Table 1 was obtained. Furthermore,
"as-depo optical constant" in the table is equivalent to the optical
constant in the amorphous state.
On the basis of the results in Table 1, in the present
invention, when the wavelength of recording/reproducing light is
within the range of 650 nm to 665 nm and the recording linear
speed is 20 m/s to 28 m/s (approximately 6X-speed to 8X-speed), a
phase-change recording material where the refractive index Nc &
the extinction coefficient Kc in the crystalline state and the
refractive index Na & the extinction coefficient Ka in the
amorphous state in the recording layer are within the following
ranges is used:
2.0 ≤Nc ≤ 3.0

4.0≤Kc≤5.0
4.0 ≤ Na ≤5.0
2.5 ≤Ka≤3.1
Furthermore, when the wavelength of the
recording/reproducing light is within the range of 650 nm to 665
nm and the recording linear velocity is 20 m/s to 28 m/s
(approximately 6X-speed to 8X-speed), the refractive index Nc &
the extinction coefficient Kc in the crystalline state and the
refractive index Na & the extinction coefficient Ka in the
amorphous state in the recording layer can be measured as
follows. Immediately after the preparation of the recording layer
composed of the phase-change recording layer with 100 nm of
thickness on a polycarbonate transparent substrate with 0.6 mm
of thickness, Na and Ka in the amorphous state in the recording
layer are measured by spectroellipsometry. Furthermore, after
the initialization of the phase-change recording layer with an
initializer, Na and Ka in the crystalline phase are measured by
spectroellipsometry. The optical constants are measured by
spectroellipsometry with a VASE and a WVASE32 software (J.A.
Woollam Japan Co., Inc.). The initializer used here is a
POP120-7AH (Hitachi Computer Peripherals Co., Ltd.). The
conditions for the initialization are 900 mW of laser power, 11 m/s
of linear velocity, and 37 p.m of head feed.

Further, an element(s) other than the four elements, Ga,
Sb, Sn and Ge, such as, Te, can be added to the optical recording
medium of the present invention. For the added quantity of the
element (atomic%), as long as the range is small to some extent,
an effect on the above-mentioned refractive index and extinction
coefficient is small, and the recording characteristic at
high-speed recording, approximately at 6X-speed to 8X-speed,
becomes excellent. The below-mentioned Table 2 shows the data
in the case that the added element is Te, and it is clear that it is
preferable to control the composition ratio at 5 atomic% or less.
Preferably the total of contents of the four elements, Ga, Sb, Sn
and Ge, in the recording layer is 95 atomic% or greater relative to
all elements in the recording layer. Te contributes to the
easiness of the initial crystallization. In addition, for the
purpose of the improvement of various characteristics, other
element, such as In, Zn, Ag or Cu, can be added.
Further, the conventional AglnSbTe-base phase-change
recording material is not suitable for high linear velocity
recording because the crystallization kinetic is slow, so the
amorphous mark cannot be accurately recorded at 6X-speed to
8X-speed. Therefore, the development of a new phase-change
recording material recordable at 6X-speed to 8X-speed is required.
Up to the present, as a recording material, a three-element

material, Ga, Sb and Sn, and the four-element material, Ga, Sb,
Sn and Ge, have been developed. However, any material
sufficiently responsive to recording at 6X-speed to 8X-speed has
not been obtained yet. Then, the inventors of the present
application have developed the phase-change recording material
responsive to recording at approximately 6X-speed to 8X-speed by
determining the composition ratio of each element within the
range of several %.
In other words, according to the research up to the present,
it has been clear that because the crystallization kinetic of the
SbSn compound is very fast, there is a possibility of realizing a
high-speed recording medium with excellent recording sensitivity.
However, the storage condition at room temperature is poor, so
the SbSn compound cannot be independently used as a recording
material. Then, if Ga or Ge is added, the amorphousness
becomes easier and it results in easy recording. Ga and Ge have
a function to slow the crystallization kinetic down, so the
crystallization kinetic can be controlled to be responsive to the
recording linear velocity at approximately 6X-speed to 8X-speed.
Therefore, in the recording layer of the present invention,
it is desirable to satisfy the following conditions regarding the
composition ratio (atomic%) of the four elements, Ga, Sb, Sn and
Ge, as a, 6, y and 8, respectively.

2 ≤ a ≤ 11
59≤B≤ 70
17≤Y≤ 26
2≤8 ≤ 12
84 ≤ B + y ≤ 88
a + B + y + 8 = 100
In the above-mentioned conditions, if Sb is less than 59 %,
the melting point becomes higher, so the sensitivity becomes poor,
and if Sb exceeds 70 %, it becomes difficult to record an
amorphous mark; thus excellent recording characteristics cannot
be obtained. If Sn is less than 17 %, the crystallization kinetic
starts slowing down, so the sensitivity becomes poor, and if Sn
exceeds 26 %, the crystallization kinetic becomes excessively fast
and it becomes difficult to become amorphous, so it is not
preferable. If Ga or Ge is less than 2 %, the storage reliability
deteriorates, and if Ga exceeds 11 % or Ge exceeds 12 %, the
crystallization temperature becomes excessively high and the
initial crystallization becomes difficult, so it is not preferable.
In addition, if a total of Sb and Sn is less than 84 % or
exceeds 88 %, it causes excessively slow or fast crystallization
kinetic, respectively, so a recording layer suitable for recording at
6X-speed to 8X-speed cannot be obtained. Examining the range
of the total composition ratio of Sb to Sn where the recording

characteristic at 8X-speed becomes excellent, as shown in Fig. 8,
the recording characteristic becomes excellent when the total of
Sb + Sn is within the range of 84 % to 88 %, and it has become
clear that if the total is out of this range, the recording
characteristic deteriorates. As described above, in order to
securely perform the high-speed recording, not only providing the
composition ratio of Sb to Sn independently, but it is also
important to provide the range of the total composition ratio of Sb
to Sn.
Fig. 1 shows comparison data of the storage stability
according to whether or not Ge is contained. As an example, in
Ga11.9Sb73.1Sn15 (a line through the diamond points in the chart),
which is phase-change recording material containing no Ge, the
reflectance after the initialization decreases by 5.7 % after 100
hours under the atmosphere at 85 % of humidity and 80 °C of
temperature, so the crystal condition is changed and recording
becomes difficult. Further, even after recording, the storage
condition at a space region deteriorates and the jitter
characteristic deteriorates. However, in Ga5Sb70Sn17Ge8 (a line
through the square points in the chart), which is a phase-change
recording material where Ge is added, the fluctuation is defused,
so the reflectance after the initialization decreased by less than
1.5 % even after 900 hours.

Fig. 2 shows the storage characteristic of the
GaSbSnGe-base phase-change recording material (jitter
characteristic after 0 time, 10 times, 1000 times of overwriting
(DOW0 (the line through the diamond points in the chart),
DOW10 (the line through the square points in the chart) and
DOW1000 (the line through the triangular points in the chart),
respectively), and no jitter fluctuation occurs even after 900-hour
storage.
For the film thickness of the recording layer, the range of 5
nm to 50 nm is desirable, and the range of 10 nm to 20 nm is more
preferable. If the film thickness is thinner than 5 nm, defects
caused by deterioration due to the repeated recording occur.
Further, if the film thickness is thicker than 50 nm, jitter
characteristics become poor.
As the first protective layer material, transparent
material where a light is efficiently transmitted through and the
melting point is 1000 °C or higher is preferable. The oxide,
nitride or sulfide is mainly used; among these, it is preferable to
use a mixture of ZnS and Si02 where the internal stress and the
absorbency index are small. Since ZnS has small thermal
conductivity, the thermal diffusion during recording can be
reduced, resulting in the increased recording sensitivity.
However, ZnS changes to a crystal at the time of initialization or

recording, deteriorating the stability of the recording layer, so a
mixture with SiO2 inhibiting the crystallization of ZnS should be
used. For the composition, it is preferable that ZnS : SiO2 = 60 :
40 to 90 - 10 (mol %). In particular, it is preferable that ZnS :
Si02 = 80 : 20 (mole ratio).
For the film thickness, the range of 30 nm to 100 nm is
desirable. If the film thickness is out of this range, it becomes
difficult to certainly secure 60 % or greater modulation factor.
Further, if the film, thickness becomes smaller than 30 nm,
because the reflectance fluctuation according to the film
thickness becomes greater, it becomes difficult to stably form the
layer, and, if the film thickness becomes thicker than 100 nm, the
deposition time becomes longer and the productivity of the
optical recording medium decreases.
As a second protective layer material, material having the
same characteristics as that of the first protective layer is
preferable.
For the film thickness, the range of 3 nm to 15 nm is
preferable. If the film thickness is less than 3 nm, defects, such
as poor recording sensitivity or the reduction of modulation factor,
may be encountered. If the film thickness is larger than 15 nm,
there is excessive heat, and an amorphous mark becomes smaller
due to the residual heat and the recording characteristic becomes

poor.
Metal material is used for the reflective layer, and metal
material, such as Al, Ag, Au or Cu, or an alloy material of these
metal materials, is often used.
For the film thickness, the range of 100 nm to 300 nm is
preferable. If the film thickness is less than 100 nm, heat
radiation efficiency may be deteriolated. Furthermore, even if
the film thickness is larger than 300 nm, the heat radiation
efficiency will not be improved, but rather the thickness of the
film become larger beyond necessity.
In the aspect where the first protective layer and the
second protective layer comprise a mixture of ZnS and Si02 and
the reflective layer comprise Ag or alloy where Ag is a main
component, it is preferable to additionally establish a sulfidation
prevention layer between the second protective layer and the
reflective layer.
Fig. 3 shows a layer construction example of the optical
recording medium of the present invention, and is a construction
where a first protective layer 2 containing the mixture of ZnS and
Si02, a recording layer 3, a second protective layer 4 containing
the mixture of ZnS and SiO2, a sulfidation prevention layer 5 and
a reflective layer 6 composed of Ag alloy are laminated in order
onto a transparent substrate 1.

A reversible phase transition between the crystal and
amorphous states of the phase-change recording layer by the
irradiation of a laser beam from the substrate side results in
recording and erasure of information. DVD+RW is in the
crystalline state before recording, and the irradiation of a
modulated laser beam and quenching of the recording layer
result in the formation of an amorphous mark. At this time, in
order to directly perform the repeated recording of the
amorphous mark, it is necessary to crystallize the amorphous
mark in shorter period as recording speed increases: therefore, a
phase-change recording material with fast crystallization kinetic
is required. Further, if using a material with fast
crystallization kinetic, re-crystallization progresses from the
periphery of the amorphous mark immediately after the mark
formation and the mark becomes smaller. In order to reduce the
re-crystallization region, it is better to have a quenching
structure where cooling velocity is fast, so it is preferable to use
Ag or alloy where Ag is a main component, which has high
thermal conductivity, for the reflective layer. Herein, the main
component means contains 90 atomic% of Ag. Further, as an

element forming alloy with Ag5 Cu, Pd, Ti, Cr and Ta are
provided.
However, Ag tends to migrate rapidly within a layer, and,

in addition, it reacts with S to easily form Ag2S. Consequently,
it is preferable to establish a sulfidation prevention layer. For
the sulfidaition prevention layer, SiC or Si, which has been
conventionally used, can be used. However, from viewpoints to
improve the adhesion between the reflective layer and the
sulfidation prevention layer and to prevent the generation of disc
defects such as the formation of loose film even after repeated
recording or the long-term storage in a severe environment, it is
preferable to use a mixture of TiC and TiO. To achieve faster
recording speed, larger recording power is required. Therefore, if
the adhesion between the sulfidation prevention layer and
ZnS-SiO2 or Ag is not strong enough, film peeling-off occurs
easily after repeated recording, compared to the optical recording
medium for low-speed recording. For SiC, since the coefficients
of thermal expansion of Ag and SiC are markedly different from
each other, the internal stress of the film increases upon the
initialization or upon recording, and the film peeling-off may
occur.
Then, using the mixture of TiO, whose coefficient of
thermal expansion is close to that of Ag, and which has good
adhesion with Ag, and TiC, which has an effect to prevent the Ag
dispersion, for the sulfidation prevention layer between the Ag
reflective layer and the second protective layer and combining

with the above-mentioned recording layer enable the provision of
an optical recording medium where the modulation factor is great,
and suitable to high-speed recording, and where the storage
stability is more excellent.
Further, setting the total film thickness of the second
protective layer and the sulfidation prevention layer at 7 nm to
20 nm enables the provision of the optical recording medium with
a greater modulation factor. More preferably, setting the total
film thickness of the above-mentioned two layers at 7 nm to 15
nm enables excellent repeated recording characteristics. In
high-speed recording, the cooling velocity of the recording layer
greatly changes of recording characteristics, so the total film
thickness of the second protective layer and the sulfidation
prevention layer, which are interposed "between the reflective
layer and the recording layer greatly affecting the cooling
velocity, is important.
It is preferable that the composition of the sulfidation
prevention layer be (TiC)p(TiO)ioo-P and 50 ≤ p ≤ 80 ('p' is % by
mass). When 'p' is 80 or less, a greater modulation factor can be
obtained, and when 'p' is 50 or greater, excellent repeated
recording characteristics can be obtained. The greater 'p'
becomes, the greater the thermal conductivity becomes.
However, if the thermal conductivity of the sulfidation

prevention layer is excessively great, the modulation factor
becomes smaller, and if the thermal conductivity is excessively
small, heating occurs and the repeated recording characteristic
becomes especially poor. The thermal conductivity and the
difference of film thickness of the layers interposed between the
reflective layer and the recording layer especially affect the
high-speed recording, so if these are not within an appropriate
range, respectively., excellent recording characteristics where
rewritable optical disc system can be realized cannot be obtained.
Further, a layer composed of a mixture of ZrO2, Y2O3, and
T102 can be established between the second protective layer and
the sulfidation prevention layer with 2 nm to 8 nm of thickness.
If using a mixture of TiC and TiO for the sulfidation prevention
layer, even though the modulation factor can easily become
smaller compared to the case of using SiC, the establishment of
the above-mentioned mixture layer increass the modulation
factor. For the composition, it is preferable to mix 60 mol % or
greater of ZrO2 and 10 mol % or greater of TiO2.
Further, it is preferable to establish an interface layer
composed of Si02 with 2 nm to 4 nm of thickness between the first
protective layer and the phase-change recording layer. This
reduces damage to a substrate when recording is performed at
high power, so the repeated recording characteristic in the high

power recording becomes excellent, and the recording power
margin can be widened. If the thickness is less than 2 nm, it
becomes difficult to form a uniform Si02 layer, and if the
thickness exceeds 4 nm, the recording sensitivity becomes poor
and the modulation factor diminishes.
For the transparent substrate, a plastic substrate is
generally used. As the plastic substrate, as long as it has
transparency and it excels in planar accuracy, there is no special
limitation. Any substrate, which has been conventionally used
as a transparent substrate for an optical recording medium, can
be optionally selected and used. As a typical example, a glass
plate and a polycarbonate plate are provided. Concerning the
optical constant, it is preferable that the refractive index be 1.5
to 1.6.
In addition, it is preferable that the transparent substrate
has a wobbled groove with 0.74 ± 0.03 urn of track pitch, 22 nm to
40 nm of groove depth and 0.2 p.m to 0.3 p.m of groove width. As
a purpose of having the wobbled groove, there are the access to an
unrecorded specific track and the rotation of the substrate at a
constant linear velocity. The optical recording medium of the
present invention is produced for the purpose of enabling
response to the recording at approximately 6X-speed to 8X-speed.
Sn is added to a GaSb'base material for the purpose of improving

the recording characteristic and accelerating the crystallization
kinetic. However, it should be noted that the effect of Sn
contained in the recording layer causes increased reflectance.
For example, as a result of researching about the optical
recording medium of the present invention where the groove
depth of the transparent substrate is 20 nm, the film thickness of
the first protective layer is 30 nm to 100 am, the film thickness of
the recording layer is 5 nm to 50 nm, the film thickness of the
second protective layer is 3 nm to 15 nm, the film thickness of the
reflective layer is 100 nm to 300 nm and the relative composition
ratios of the four elements in the recording layer fulfill the
above-mentioned requirement, it has become clear that the
reflectance at an unrecorded region (crystalline substance)
becomes within the range of 26 % to 32 %. However, if
comparing this reflectance with reflectance at lX-speed to
4X-speed of DVD+RW, which is a conventional phase-change
optical recording medium, it is unnecessarily high. Therefore,
taking the compatibility into consideration, it is necessary to
adjust the reflectance by reduction.
Therefore, the conditions of the transparent substrate
having the wobbled groove with 0.74 ± 0.03 µm of track pitch, 22
nm to 40 nm of the groove depth and 0.2 µm to 0.3 µm of groove
width are adopted. For example, researching about the

transparent substrate by setting the groove depth at 37 nm, the
reflectance could be reduced by approximately 2 % to 3 %. In the
DVD disc having track pitch at 0.74 ± 0.03 am, a push-pull signal
is mainly extracted as a signal used for detecting a tracking error.
For the push-pull signal, at 660 nm of laser wavelength used for a
DVD, the greatest signal intensity can be obtained if using the
above-mentioned transparent substrate when the groove depth is
55 nm. In order to adjust the reflectance to be low and to
increase the amplitude of an error signal, for the groove depth,
the deeper the better. However, also taking the recording
characteristic into consideration, it is preferable that the groove
depth is within the range of 22 nm to 40 nm. Further, taking the
recording characteristic and the signal characteristic into
consideration, it has become clear that it is desirable for the
groove width to be within 0.2 µm to 0.3 µm.
The present invention can provide a DVD+RW medium
that enables the repeated recording at 20 m/s to 28 m/s
(approximately 6X-speed to 8X-speed), and where the recording
characteristic and storage characteristic are also excellent, and
in addition, a DVD+RW where the reflectance of the recording
layer is appropriately reduced.
Hereafter, the present invention is more specifically
described using Examples and Comparative Examples. However,

the present invention will not be limited by these Examples.
[Examples A-l to A-7 and Comparative Examples A-8 to A-19]
Discs where the first protective layer ZnS-Si02 with 60 nm
of thickness, the recording layer composed of the phase-change
recording material shown in Table 1 with 16 nm of thickness, the
second protective layer ZnS_Si02 with 7 nm of thickness, the
sulfidation prevention layer SiC with 4 nm of thickness and the
reflective layer Ag with 140 nm of thickness were laminated in
this order on a polycarbonate transparent substrate having 0.74
p,m of track pitch, 27 nm of groove depth and 0.27 µm of groove
width were prepared. These discs were initialized using an
initializer for a phase-change disc, and a DVD+RW disc was
obtained. For the initialization, an optical head with 48 nm of
beam width was used, and crystallization was conducted under
the conditions with 1300 mW of power (herein, it is power
consumption of LD, and this is different from an irradiation
power), 18.5 m/s of scanning speed and 30 µm/rotation of feed.
The recording layers of the above-mentioned discs are all
composed of the GaSbSnGe-base material with various optical
constants having sufficient transfer linear velocity at 20 m/s or
faster. For these discs, the recording linear velocity was set at
6X-speed (20.9 m/s) and 8X-speed (27.9 m/s), and whether or not
excellent recording characteristics could be obtained was

examined. Recording was performed by repeating the intensity
modulation, with 2T cycle recording strategic having three levels
(Pp > Pe > Pb), peak power 'Pp1 for the purpose of forming an
amorphous mark, bottom power 'Pb' for the purpose of providing
a quenching efficacy and erasure power 'Pe' for the purpose of
forming crystalline substance and erasing the information. A
pulse generator is DTG-5274 manufactured by Tektronix
Japan,Ltd., and the set resolving power is 3.348352 GHz. The
evaluation device for this recording is DDU-1000 manufactured
by Pulstec Industrial Co., Ltd and the specifications of the
recording power are 40 mw with Pp at maximum and 18 mW with
Pe at maximum. The peak power Pb was fixed at 0.1 mW and
recording was performed. Numerical values used for criteria for
the purpose of determining appropriateness of the recording
characteristic are "Data to Clock Jitter (hereafter, referred to as
DC jitter)"' and "modulation factor". The DC jitter is digitization
of the gap of ends between the window 'Tw' upon reproducing at
IX speed (corresponding mark length is approximately 0.1333
µm) and nine types of marks regarding the window width Tw as
unit (3Tw to 11Tw marks), and it means that the smaller the
value becomes, the better the characteristic becomes. The
modulation factor indicates how much the difference of the
reflectance between a crystalline substance and an amorphous

substance is occupied relative to the reflectance of the crystalline
substance. Since the greater difference of the crystalline
substance can be easily binarized, for the modulation factor, the
greater the better. The evaluation criteria are as follows, and
the numerical values are values after 10 times of overwriting
(DOW10): A: 9 % or less, B: 11 % or less, C: over 11 % A: 60 % or greater, B: less than 60 %

composition ratio (atomic%) of Sb to Sn>
With respect to discs in Example A'2 and the
below-mentioned Examples A-20 to A-23, the recording
characteristics were compared.
For the discs in Examples A-2, A-20 and A-21, Fig. 4 shows
the compared result of the DC jitter after DOW10 at 8X-speed in
the case of changing the peak power (Example A-2- the line
through the triangular points, Example A-20: the line through
the diamond points, and Example A-21- the line through the
rectangular points), and Table 1 shows the result in Examples
A-22 andA-23.
The recording characteristic of the disc in Example A-2 (Sb
+ Sn = 81.8 atomic%) was evaluated, and the bottom jitter after
DOW10 at 6X-speed and 8X-speed was 8.9 % and 13.9 %,
respectively.
[Example A-20]
A disc was prepared similarly to Example A-l except for
changing the phase-change recording material to Ga7Sb69Sn18Ge6
(Sb + Sn = 87 ato:mic%, Nc = 2.25, Kc = 4.90, Na = 4.30, Ka = 3.01),
and the recording characteristics were evaluated. The bottom
jitter after DOW10 at 6X-speed and 8X-speed was 7.9 % and 7.7 %,

respectively; thus excellent characteristics were obtained.
according to groove depth>
With respect to each disc in Examples A-3, A-24 and A-25,
Fig. 5 to Fig. 7 show the comparison results of the DC jitter, the
modulation factor and the reflectance in the case of changing the
peak power (Example A-3 (groove depth: 27 nm): the line through
the rectangular points, Example A-24 (groove depth: 37 nm)'- the
line through the diamond points, Example A-25 (groove depth: 42
nm): the line through the triangular points), respectively.
The bottom jitter of the disc in Example A-3 after DOW10
at 6X-speed and 8X-speed shown in Table 1 was 8.0 % and 8.4 %,
respectively, and the modulation factor was also excellent, which
was 61.5 %, and the reflectance at an unrecorded region (R14H)
at that time was 26.5 %.
[Example A-24]
A disc was prepared similarly to Example A-3 except for
changing the groove depth of the substrate, to 37 nm, and the
recording characteristics were evaluated. The bottom jitter
after DOW10 at 6X-speed and 8X-speed was 8.2 % and 8.6 %,
respectively, and the modulation factor was excellent, which was
61.7 %, and the reflectance at an unrecorded region (R14H) at

that time was 24.4 %.
[Example A-25]
A disc was prepared similarly to Example A-3 except for
changing the groove depth of the substrate to 42 nm, and the
recording characteristics were evaluated. The bottom jitter
after DOW10 at 6X-speed and 8X-speed was 9.7 % and 10.2 %,
respectively, so both showed slight deterioration, and the
modulation factor was 61.6 % and the reflectance at an
unrecorded region (B.14H) at that time was 22.1 %. Although
lower reflectance could be obtained, the recording characteristics
had slightly deteriorated.
[Example A-26]
A disc was prepared similarly to Example A-l except for
changing the phase-change recording material to
Ga7Sb68Sn15Ge6Te4, and the recording characteristics were
evaluated. The result is shown in Table 2.
[Example A-27]
A disc was prepared similarly to Example A-l except for
changing the phase-change recording material to
Ga5Sbt68Sn15Ge7Te5, and the recording characteristics were
evaluated. The result is shown in Table 2.
[Example A-28]

A disc was prepared similarly to Example A-l except for
changing the phase-change recording material to
Ga3Sh68Sn15Ge8Te6, and the recording characteristics were
evaluated. The result is shown in Table 2.
[Example A-29]
A disc was prepared similarly to Example A_l except for
changing the phase-change recording inaterial to
Ga3Sb67Sn14Ge8Te8, and the recording characteristics were
evaluated. The result is shown in Table 2.

As it is clear from the above-mentioned Table 2, Nc
exceeded 3.0 in Comparative Examples A-28 andA-29, and
preferable results could not be obtained for both the jitter and
the modulation factor.
According to the above-mentioned Examples and
Comparative Examples, it has been demonstrated that using the
GaSbSnGe-base phase-change recording layer material having
optical constants provided in the present invention enables
recording at 6 X-speed to 8X-speed of recording linear veloCitY.
Further, according to Examples A-2 and A-20 to A_23, it is clear
that if the total composition ratio of Sb to Sn is within the range
of 84 ≤6 +. y ≤ 88, further excellent recording characteristic and
storage stability can be obtained.
Further, according to Examples A-3, A-24 and A-25, in the
case that the transparent substrate has a wobbled groove with
0.74 ± 0.03 µm of track pitch, 22 nm to 40 nm of groove depth and
0.2 µm to 0.3 µm of groove width, it is clear that while excellent
recording characteristics are maintained, the reflectance can be
controlled to be low.
(Examples B-l to B-7)

The first protective layer, the phase-change recording
layer, the second protective layer, the sulfidation prevention
layer and the reflective layer were deposited in order onto a

polycarbonate substrate with 0.74 µm of track pitch, 27 nm of
groove depth, 12 cm of diameter and 0.6 mm of thickness
according to the sputtering method.
For the first protective layer, (ZnS)8o(Si02)2o (mol %) was
used as a target and the film thickness was set at 60 nm.
For the phase-change recording layer, Sn18Sb68Ga5Ge9
(atomic%), Nc = 2.33, Kc = 4.88, Na = 4.45, Ka = 2.89, was used as
a target and the film thickness was set at 16 nm.
For the second protective layer, (ZnS)80(Si02)20 (mol %)
was used as a target and the film thickness was set as shown in
Table 3.
For the sulfidation prevention layer, (TiC)7o(TiO)3o
(mass %) was used as a target and the film thickness was set as
shown in Table 3.
For the reflective layer, Ag was used as a target and the
film thickness was set at 180 nm.
Subsequently, after applying acrylic-base cured resin
(SD318 manufactured by Dainippon Ink and Chemicals,
Incorporated) with 8 µm of thickness onto the reflective layer
according to the spin coating method, the film was cured by
ultraviolet ray in an N2 atmosphere and a resin protective layer
was formed.
In addition, another polycarbonate substrate with 12 cm of

diameter and 0.6 mm of thickness was bonded onto the resin
protective layer using an adhesive, and a disc-shaped optical
recording medium was obtained.
Subsequently, the optical recording medium was
initialized using an initializer (POP120-7AH manufactured by
Hitachi Computer Peripherals Co., Ltd.) having a laser head
where a focusing function was added to a. laser beam with 830 nm
of output wavelength, approximately 1 µm of width, 75 µm of
length and 2W of maximum output. Fixed initialization
conditions were 1500 mW of laser output, 20 m/s of scanning
speed and 50 µm of head feed.

With respect to the optical recording media prepared as
mentioned above, recording and reproducing were evaluated
using the optical disc evaluating device (DDU-1000

manufactured by Pulstec Industrial Co., Ltd) having a pickup
with 650 nm of wavelength and 0.65 of NA. The recording linear
velocity was set at 28 m/s (equivalent to 8X-speed of DVD), the
jitter (data to clock jitter: a value where 'a' is standardized with
detection window width 'Tw') when repeatedly recording the
random pattern 10 times with EFM + modulation method and the
modulation factor are shown in Table 4. The recording strategy
was optimized, and reproducing was all performed at 3.5 m/s of
linear velocity with 0.7 mW of power.

As it is clear from Table 4, in the case that the total film
thickness of the first protective layer and the sulfidation
prevention layer is especially 7 nm to 20 nm, 60 % or greater
modulation factor, which is a standard value for DVD-ROM, could
be obtained. In addition, in the case that the total film

thickness is 7 nm to 15 nm, the jitter after 10 times of repeated
recording was within 9 %, which is a standard value; thus
preferable repeated recording characteristics could be obtained.
In the case that the total film thickness was less than 7 nm, the
modulation factor was small and the jitter was 9 % or greater.
This was because heat was not sufficiently applied to the
recording layer, the fused region was narrow, and the formed
mark was small. Further, in the case that the total film
thickness exceeded 20 nm, the modulation factor was also small
and the jitter was also 9 % or greater, because even though the
fused region was wide, the period of time to be maintained in the
temperature range where re-crystallization occurs was long, so
re-crystallization progressed.from the periphery of the mark, and
as a result, the formed mark became small.
In addition, after storing each of the above-mentioned
optical recording media for 100 hours in an environment of 80 °
and 85 % RH, the optical recording media were visually observed
by holding each of them to a lamp, and no pinhole generation was
confirmed in any of them.
Furthermore, the transfer linear velocity of the recording
medium in Example B-l was 28 m/s.
(Examples B-8 to B-12)
Disc-shaped optical recording media were prepared

similarly to Example 1 except for changing the phase-change
recording material to Sn13Sb72Ga7Ge8, Nc = 2.21, Kc = 4.97, Na =
4.36, Ka =: 2.98, setting the film thickness of the first protective
layer at 8 nm and the film thickness of the sulfidation prevention
layer at 5 nm, and changing the composition of the sulfidation
prevention layer to that shown in Table 5.
With respect to these optical recording media, recording
and reproducing were evaluated using the optical evaluating
device (DDU-1000 manufactured by Pulstec Industrial Co., Ltd)
having a pickup with 650 nm of wavelength and 0.65 of NA. The
recording linear velocity was set at 28 m/s (equivalent to
8X-speed of DVD), and the modulation factor upon repeatedly
recording a random pattern 10 times with EFM + modulation
method and the jitter upon repeatedly recording 1,000 times were
examined. If the jitter was greater than 9 %, the optical
recording medium was graded as B, and if the jitter is 9 % or less,
the medium was graded A, and the result is shown in Table 5.
As it is clear from Table 5, in the case that TiC was 80 (%
by mass) or less, the modulation factor after DOW10 was 60 % or
greater. Further, in the case that TiC was 40 (% by mass), the
modulation factor was greater, but the jitter after DOW1000 was
9 % or greater.
Furthermore, the transfer linear velocity of the recording

(Example B-13)
Disc-shaped optical recording media were prepared
similarly to Example B-3 except for changing the phase-change
recording material to SnaoSbssGasGeio (Nc = 2.43, Kc = 4.80, Na =
4.40, Ka -- 2.78 and the transfer linear velocity = 26 m/s).
With respect to this optical recording medium, recording
and reproducing were evaluated using the optical disc evaluating
device (DDU-1000 manufactured by Pulstec Industrial Co., Ltd)
having a pickup with 650 nm of wavelength and 0.65 of NA. The
recording linear velocity was set at 28 m/s (equivalent to
8X_speed of DVD), and it was optimized with 32 mW of recording

power Pw, 0.1 mW of bottom power Pb, and 5 mW to 10 mW of
erasing power Pe. A random pattern was repeatedly recorded
with EFM + modulation method and the jitter (data to clock
jitter: a value where 'a' was standardization with detection

window width. 'Tw') was evaluated. The recording strategy was
optimized, and reproducing was all performed at 3.5 m/s of linear
velocity with 0.7 mW of power.
In addition, after this optical recording medium was
stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same condition. Each result
is shown in Fig. 9 (before the storage test: the line through the
rectangular points, after storage test: the line through the
diamond points).
As it is clear from Fig. 9, even after 100-hour storage in an
environment of 80° and 85% RH, no great jitter deterioration was
confirmed. The optical recording medium after this storage test
was visually observed by holding it to a lamp; however, no
pinhole generation was confirmed.
(Example B-14)
A disc-shaped optical recording medium was prepared
similarly to Example B-13 except for changing the phase-change
recording material to Sn20Sb65Ga3Ge7Te5, (atomic%), Nc = 2.50, Kc
= 4.80, Na = 4.35, Ka = 2.68, the transfer linear velocity = 24 m/s,
and changing the film thickness of the second protective layer to
10 nm. Recording was performed similarly to Example B-13,
and the jitter after DOWl was improved more than that in
Example B-13. It is considered that because the addition of Te

resulted in the uniform initial crystallization, the jitter rise after
DOW1 was diminished.
In addition, after this optical recording medium was
stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same condition. Each result
is shown in Fig. 10 (before the storage test: the line through the
rectangular points, after storage test'- the line through the
diamond points).
As it is clear from Fig. 10, even after 100-hour storage in
an environment of 80 °C and 85% RH, no great jitter
deterioration was confirmed. The optical recording medium
after this storage test was visually observed by holding it to a
lamp; however, no pinhole generation was confirmed.
(Example R-15)
An optical recording medium was prepared under similar
conditions to those in Example B-13 except for changing the
phase-change recording material to Sn16Sb70Ga6Ge8 (atomic%)
(Nc = 2.43, Kc = 4.90, Na = 4.36 and Ka = 2.97, and the transfer
linear velocity = 27 m/s), changing the film thickness of the
second protective layer to 5 nm, targeting (TiC)eo(TiO)4o (% by
mass) for the sulfidation prevention layer, and changing its film
thickness to 3 nm. Recording was performed similarly to
Example B-13, and the jitter decreased by 0.5 % compared to that

in Examples B-13.
In addition, after this optical recording medium was
stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same condition. No great
jitter deterioration was confirmed. The optical recording
medium after this storage test was visually observed by holding
it to a lamp; however, no pinhole generation was confirmed.
(Example B-16)
An optical recording medium was prepared under similar
conditions to those in Example B-13 except for changing the film
thickness of the first protective layer to 70 nm, changing the
phase-change recording material to Sn19Sb63Ga9Ge9 (atomic%)
(Nc = 2.21, Kc = 4.61, Na = 4.31, Ka = 2.88, and the transfer
linear velocity = 22 m/s), changing its film thickness to 14 nm,
changing the film thickness of the second protective layer to 4 nm,
targeting (TiC)50(TiO)50 (% by mass) for the sulfidation
prevention layer, and establishing a layer containing a mixture of
Zr02,Y203, and T1O2 with 3 nm of film thickness between the
second protective layer and the sulfidation prevention layer.
Recording was performed similarly to Example B-13, and the
jitter characteristic, which was the same level as that in Example
13, was obtained, and the modulation factor increased by 2 %.
In addition, after this optical recording medium was

stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same condition. No great
jitter deterioration was confirmed. The optical recording
medium after this storage test was visually observed by holding
it to a lamp; however, no pinhole generation was confirmed.
(Example B-17)
An optical recording medium was prepared under similar
conditions to those in Example B-13 except for changing the film
thickness of the first protective layer to 58 nm, establishing an
Si02 layer with 2 nm of film thickness between the first
protective layer and the phase-change recording layer, changing
the phase-change recording material to Sn14Sb68Ga10Ge8
(atomic%) (Nc = 2.38, Kc = 4.87, Na = 4.38, Ka = 2.55, and the
transfer linear velocity = 24 m/s), changing its film thickness to
14 nm, changing the film thickness of the second protective layer
to 4 nm, and changing the film thickness of the sulfidation
prevention layer to 6 nm. Recording was performed similarly to
Example B-13, and the repeated recording characteristic upon
recording with higher power than that of Example B-13 was
improved.
In addition, after this optical recording medium was
stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same condition. No great

jitter deterioration was confirmed. The optical recording
medium after this storage test was visually observed )by holding
it to a lamp; however, no pinhole generation was confirmed.
(Examples B-18)
An optical recording medium was prepared under similar
conditions to those in Example B-13 except for changing the film
thickness of the second protective layer to 10 nm and changing
the sulfidation prevention layer material to SiC. Recording was
performed similarly to Example B-13, and the jitter
characteristic, which was the same level as that in Example B-13,
was obtained. However, after this optical recording medium was
stored for 100 hours in an environment of 80 °C and 85 % RH,
recording was performed under the same conditions, and when
the optical recording medium after this storage test was held to a
lamp, pinholes were visually observed. Furthermore, the transfer
linear velocity of the recording medium in Example B-18 was 26
m/s, Nc = 2.37, Kc = 4.82, Na = 4.45, and Ka = 2.88).
(Comparative Example B-l)
An optical recording medium was prepared under similar
conditions to those in Example B-13 except for changing the
phase-change recording material to Ag5ln5Sb65Te25 (atomic%) and
changing the film thickness of the second protective layer to 10
nm. Recording was performed similarly to Example B-13;

however, recording could not be repeatedly performed. The
optical recording medium after this storage test was visually
observed by holding it to a lamp, and no pinhole generation was
confirmed.

We Claim:
1. An optical recording medium comprising:
a transparent substrate,
a first protective layer disposed on the transparent substrate,
a recording layer disposed on the first protective layer,
a second protective layer disposed on the recording layer, and
a reflective layer disposed on the second protective layer,
wherein when the wavelength of a recording and reproducing
light is within the range of 650 nm to 665 nm and the recording linear
velocity is 20 m/s to 28 m/s, the refractive index Nc and the extinction
coefficient Kc in a crystalline state and the refractive index Na and the
extinction coefficient Ka in an amorphous state in the recording layer
respectively satisfy the following numerical expressions:
2.0≤ Nc≤ 3.0,
4.0≤ Kc≤ 5.0,
4.0≤ Na≤ 5.0, and
2.5≤Ka≤ 3.1, and
wherein information is recordable at the range of 20 m/s to 28
m/s of recording linear velocity,
wherein the optical recording medium comprises a sulfidation
prevention layer between the second protective layer and the reflective
layer; and the first protective layer and the second protective layer

comprises a mixture of ZnS and Si02, respectively, the reflective layer
comprises Ag or an alloy where Ag is a main component, characterized
in that the sulfidation prevention layer comprises a mixture of TiC and
TiO, and the recording layer is composed of a phase-change recording
material comprising Ga, Sb, Sn and Ge, and the transfer linear velocity
is 20 m/s to 30 m/s,
2. The optical recording medium as claimed in claim 1, wherein
when the mutual composition ratios (atomic%) of the four elements, Ga,
Sb, Sn and Ge, in the recording layer are regarded as a, 6, y and 8,
respectively, these satisfy the following numerical expressions:
2≤a≤ll,
59≤ 8≤ 70,
17≤y≤26,
2≤8≤12,
84≤ 6 + y≤ 88, and
a + B + Y + 8= 100.
3. The optical recording medium as claimed in claim 2, wherein
the total of contents of the four elements, Ga, Sb, Sn and Ge, in the
recording layer is 95 atomic% or greater relative to all elements in the
recording layer.
4. The optical recording medium as claimed in claim 3, wherein

the recording layer comprises Te.
5. The optical recording medium as claimed in any one of claims
1 to 4, wherein the film thickness of the first protective layer is 30 nm
to 100 nm, the film thickness of the recording layer is 5 nm to 50 nm,
the film thickness of the second protective layer is 3 nm to 15 nm and
the film thickness of the reflective layer is 100 nm to 300 nm.
6. The optical recording medium as claimed in any one of claims
1 to 5, wherein the transparent substrate has a wobbled groove with
0.74 ± 0.03 µ.m of track pitch, 22 nm to 40 nm of groove depth and 0.2
µm to 0.3 µm of groove width.
7. The optical recording medium as claimed in any one of claims
1 to 6, wherein the total film thickness of the second protective layer
and the sulfidation prevention layer is 7 nm to 20 nm.
8. The optical recording medium as claimed in claim 7, wherein
the total film thickness of the second protective layer and the
sulfidation prevention layer is 7 nm to 20 nm.
9. The optical recording medium as claimed in any one of claims
1 to 8, wherein wherein the composition of the sulfidation prevention

layer is (TiC)p(TiO)10o-p, wherein 'p' represent percentage by mass and
satisfy the following numerical expressions, 50≤ p≤ 80.
10. The optical recording medium as claimed in any one of clain
1 to 9, wherein the optical recording medium comprises a layer
containing a mixture of Zr02, Y203, and Ti02 with 2 nm to 8 nrn of fil:
thickness between the second protective layer and the sulfidation
prevention layer.
11. The optical recording medium as claimed in any one of clain
1 to 10, wherein the optical recording medium comprises a layer
containing Si02 with 2 nm to 4 nm of film thickness between the first
protective layer and the phase-change recording layer.

The invention discloses an optical recording medium having a transparent substrate 1,
a first protective layer 2, a recording layer 3, a second protective layer 4 , a sulfidation
prevention layer 5, and a reflective layer 6, wherein the recording layer 3 comprises Ga,
Sb, Sn and Ge, and where the transfer linear velocity is 20 m/s to 30 m/s, wherein the
wavelength of a recording and reproducing light is 650 nm to 665 nm and the recording
linear velocity is 20 m/s to 28 m/s, the refractive index Nc and the extinction coefficient
Kc in a crystalline state and the refractive index Na and the extinction coefficient Ka in
an amorphous state in the recording layer respectively satisfy 2.0≤ Nc≤ 3.0, 4.0≤ Kc≤
5.0, 4.0≤ Na≤ 5.0, and 2.5≤ Ka≤ 3.1, the sulfidation prevention layer 5 has a mixture of
TiC and TiO.